Functionally important regions of glucose‐6‐phosphate dehydrogenase defined by the Saccharomyces cerevisiae enzyme and its differences from the mammalian and insect forms

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Abstract
The primary structure of Saccharomyces cerevisiae glucose‐6‐phosphate dehydrogenase has been determined. It consists of 503 amino acid residues, with an acetyl‐blocked N‐terminus. The structure shows equally extensive differences from the corresponding mammalian and fruit fly enzymes (52% residues non‐identical). Residues conserved in all the forms constitute about 40% of the structures and include two histidines. One of these (His200 in the numbering of the rat enzyme) occurs in a 10‐residue conserved segment, including the reactive Lys204, probably related to substrate binding. Two segments with conserved Gly‐Xaa‐Xaa‐Gly‐Xaa‐Xaa‐Gly/Ala pattern constitute possibilities for the coenzyme‐binding site. One is N‐terminally located (positions 37–43) with two conserved arginine residues nearby (positions 56 and 71), of interest for phosphate binding. The other (positions 241–247) is in a middle region, with many residue identities, containing the conserved residues Arg256 and His264.